Recovery of sulphur



Patented July 11, 1933 UNITED, STATES PATENT "OFFICE RAYMOND F. BACON, .OF BRONXVILL E, AND HENRY T, HOTCHKISS, JR., OF NEW ROCHELLE, NEW YORK; SAID HOTCHKISS, JR., ASSIGNOR TO SAID BACON RECOVERY or SULPHUR No Drawing. Application mea September This invention relates to the production of sulphur, and more particularly to therecovery in elemental form of the sulphur liberated in the smelting of sulphide ores. x

5 The smelting of pyritic and other sulphide ores, as ordinarily conducted, results in the liberation of considerable quantities of sulphur gases, which, from a smelting standpoint, simply present a highly objectionable disposal nuisance.

As first liberated in the ore charge, the sulphur gases are comprised partly of sulphur presents no corresponding advantage to the smelting operation, but as a matter of fact constitutes a distinctly objectionable nuisance to the feeding operators.

If a practical and economical process were available which, without interfering in the smelting operation, would efiectivel-y prevent this depletion of the large amount of elemental sulphur originally liberated as'an incident to the smelting, and in addition, would permit recovery of the sulphur from the sulphur dioxide, not only would the smelting art be benefited by theelimination of the noxious gas'nuisance, but an important and extensive source of sulphur would be opened up as well. j I

It is an object of our invention to provide such a process which will reduce the sulphur dioxide from the combustion zone to ele mental sulphur, and at thesame time protect against any subsequent oxidation, the sulphur so formed as well as thatv produced by volatilization.

The manner in which we accomplish the 8, 1930. Serial no. 480,625.

same comprises in general, introducing a re: ducing gas for the sulphur dioxide at a point in the charge above the combustion zone but materially below the top of the charge, and providing this reducing gas in amount sufficient to reduce the sulphur dioxide while maintaining the reduced and volatile elemental sulphur in anon-oxidizing atmosphere, at least for the period when conditions existwhich would otherwise resultin its oxidation.- It is a further object of our invention to provide a process of the order just noted,-,wh1ch, in addition, w1ll simultaneously enhance the efficiency of the smelting opera tion itself specifically, by preheating the charge lying above the combustion zone.

In pyritic smelting, preheating the charge is generally recognized to be quite desirable,

pelled to operate on a rigid heat conserva- 7 tion basis as regards the combustion zone. for full blow pipe action concentrated in a restricted zone, is essential to the attainment of the exceedingly high temperature necessary in the smelting. Consequently, any attempt to extend the oxidizing effect beyond. such a restricted zone meets with objection.

Taking the case of the volatile sulphur which is liberated in the upper part of the charge, for example, this would constitute an excellent fuel for preheating, but the ex tension of the combustion to this source of fuel cannot be resorted to. This is due to the difliculty, if not impossibility, of limiting such combustion to the free sulphur atom and not permitting it to extend to the accompanying'i'ron sulphide. The latter sulphur must be left substantially int-actif'the. strict fuel requirements of the combustion zone are to be met. that the valuable source of fuel provided by the volatile sulphur atom must be allowed to pass off as waste, and the preheating of the It is for this reason principally,

This we accomplish by utilizing as the reducing gas for the sulphur dioxide, a gas which reacts with thesulphur. dioxide with the liberation of heat, preferably in a strong- 1y exothermic manner.

The process-of our invention may be carried out substantially as follows:

The sulphide ore to be smelted, for example chalcopyrite, prgyidedwith a suitable amount of slaggingihaterial suchas silica and as in ordinary pyritic smelting, coke in small amount, is fed into a blast furnace smelter of any well-known type, for example the common. water-jacketed pyrites smelter,

preferably provided with a closed top, and a uniform depth of bed is mantained by periodic admission of additional quantities of the charge. 1 a

The air blast is introduced through the tuyeres in the well-known manner and the resulting intense combustion of the charge adjacent the same will produce the characteristic hot focus, having for example, a temperature of 1300 C. and usually higher.

In this combustion zone, the ore is smelted with the formation of a copper matte and a slag, which pass downwardly and are tapped off at the bottom of the bosh. v

The hot gases from the combustion zone, comprising substantial amounts of sulphur dioxide formed by thecombustion of the sulphur not retained for matte formation, are

blown upwardly through the charge and serve to heat the same in its downward passage. In the upper portions of the furnace the feeble sulphur atom of the pyrites is volatilized by'the ascending heat, ultimately leaving the pyrites in what is known as the pyrrhotite or Fe-FeS form which contains the non-volatile sulphur. The temperature of the partially de-sulphurized ore is gradu- 1 ally elevated in its downward passage until it finally melts, and subsequently it flows into the-zone of intense combustion at the focus.

The oxidizing range of the combustion zone has been found to extend over but a relatively limited range, and a non-oxidizing atmosphere has been shown to begin at a point thereabove which is slightly below the point where the pyrrhotite form begins to melt.

In accordance with the process of our invention, the reducing gas used is introduced into the charge at a point materially below the top of the same but above the oxidizing range of the combustion zone, and preferably slightly above the point at which the pyrrhotite form melts, although .it may be introduced below this melting zone is desired.

By introducing it above the point where the pyrrhotite form melts, the gas will not only or'other suitable fluid reagent which will reduce the sulphur dioxide with the liberation of substantial amounts of heat, and is introduced through an auxiliary set of tuyeres disposed at the point noted, above the usual tuyeres in a water jacketed pyritic smelter or other suitable type of furnace.

If necessary or desirable, the gas may be preheated prior to its introduction into the charge, and this may be accomplished by bypassing it in contact with the hot discharge gases from the furnace and/or by auxiliary combustion of a portion of the gas, or in any other suitable manner. I

The temperature, nature and amount of the reducing gas introduced, should be so determined that the heat produced upon reaction with the sulphur dioxide, will not result in the elevation of the temperature of the charge to a degree (for example, 900-950 C.) where substantial sintering might result too near the top of the charge. The objection to such incipient fusion however, becomes less the lower down in the charge it. occurs, in View of the ultimate melting of the material which is sought, prior to its passage to the combustion zone. If desired, the normal height of the charge may be materially i11- creased.

The specific amount of reducing gas should be such as to provide not only a suitable reacting quantity for the sulphur dioxide, but also a suflicient surplus to assure the maintenanceof at least a non-oxidizing atmosphere, although it may be distinctly reducing if desired, for both the elemental sulphur producer by the reduction and by volatilization from the pyrites. In case the reducing fluid is an oil it must not be introduced in such quantity that anyoil escapes from the furnace with the sulphur, as oil contamination of sulphur is very undesirable.

The surplus of reagent will vary with the particular conditions existing in the furnace at the time, and with the nature of the reducing fluid used.

Under some circumstances, for example with suitable sealing of the furnace and the charge feeding device, and the existence of a sufficiently high gas pressure in the furnace, the amount of excess or external air to be combatted may be more or less negligible and the surplus of reducing gas correspondingly slight. Under other circumstances where external or excess air from the tuyeres may be present in material quantity, suitable quantitative provision therefor shziuld be made in the reducing gas admitted;

A fair indication of the necessary quantitative regulation of the reducing gas will be afforded by the nature of the gases being discharged from the furnace as to their content of oil or other reducing fluid, and with particular reference totheir sulphur dioxide content, as will be apparent to one skilled in the art.

By proceeding in accordance with the foregoing, practically all of the liberated sulphur which is not required for matte formation in the smelting proper, can be recovered in the elemental form and subsequently separated from the accompanying W hen carefully conducted moreover, th sulphur recovery reactions may be'practically completed within the furnace, for the reaction between the sulphur dioxide and the reducing gases particularly, is very rapid under the conditions existing therein. Even a colorablc observance of the essential factors however,will

ordinarily result in substantial progress ofthe sulphur producing reactions within'the furnace and these can be made to proceedto completion after the gases have left thefu'r uace. Where necessary or desirable, the reac tions in the furnace ases may be subjected to catalytic action after leaving the furnace as noted hereinafter. i

The discharge gases from the furnace will contain, in addition to the elemental sulphur, varying amounts of carbon dioxide, carbon monoxide, nitrogen, hydrogen sulphide, steam, hydrogen, some slight amounts of unreacted sulphur dioxide and under some circumstances a slight amount of carbon oxysulphide, the presence and amounts of these rariruis constituents depending upon the nature of the material used and the reaction conditions existing at the time. I

' The carbon oxysulphide will ordinarily be more or less decomposed by the action of the steam and hydrogen. contained in the gases, If such is not sufficient however, an additional amount of steam may be introduced either with the reducing or thereafter, if desired.

These hot effluent furnace gases are conducted to a oust collector of any well known type, for example a baffle chamber or electrostatic precipitator, and the dust-free gases are then passed to apparatus for condensing and separating sulphur. For this purpose, a

waste heat boiler or an electrostatic precipitator or both may be used, as well as other suit able and well known means.

I The residual gases from the sulphurseparation may then, or prior to the sulphur separation if desired, be treated for the recovery of further values or the removal of noxious constituents, if suchis necessary or desirable. The particular treatment to which they will be'subjected, will depend upon the nature of the residual constituents.

If, for example, an appreciable amount of hydrogen sulphide is present, this may be catalytically' oxidized, with bauxite or the like, to water and free sulphur, by reaction with air and/or sulphur dioxide, already present in or supplied to the residual gases-for that purpose.

Such catalytic oxidation with bauxite may likewise be applied to the decomposition of any carbon oxysulphide which may be present. Reaction with sulphur dioxide for example, added to the gas for this purpose if an insufficient amount isv present therein, furnishes one satisfactory means of removt: f' charging the waste gases.

Further, where any appreciable amount of sulphur dioxide still exists in the gases, its reaction with the surplus reducing gas for example, is likewise very susceptible to the catalytic effect of bauxite even though the temperature has fallen considerably below that prevailing when the gases left the furnace.

Such sulphur as is produced by these auxiliary operations, may be recovered by the use of an electrostatic precipitator or other suitableand well lmown means.

While the process of our invention is of in his objectionable constituent before dis greater practical value in true pyritic smelting, wherein substantial amounts of combustible and volatilizable sulphur are present and but little auxiliary carbonaceous fuel in the form of coke is necessary, it is likewise applicable with advantage in so-called partial pyritic smelting as well. V

In partial pyritic smelting, larger amounts of coke are used than in the true pyritic smelting operation, for the purpose of supplementing the insuflicient supply of combustible sulphur fuel. type of smelting, the matter of preheating is even more desirable than in true pyritic smelting. I

- In the prior practice this has usually been confined to preheat-in the air blast intro duced through the tuyeres, for while burning an additional amount of coke would provide additional heat for. preheating the charge, such procedure cannot be resorted to because of rigorous technical objections;

principal of which is the fact that the least Consequently, in this be obtained. No preheating expedient can ordinarily be availed .of which would'be accomplished at the expense of the oxygen in the combustion zone. 7

By the process of our invention however, a means is provided for supplementing the heat of the charge with a material cheaper than coke along with recovering the sulphur, without detriment to the proper functioning of the combustion zone, viz.; by introducing a reducing gas above the combustion zone, which will react with the sulphur dioxide produced in an exothermic manner.

By this process of our invention, it is made possible to recover practically all of the sulphur liberated in the usual smelting opera-- tion; with abatement of the nuisance heretofore constituted by the liberation of such fumes; and not only with non-interference furnace charge at a point slightly above the point at which the ore from which the volatile sulphur has beein driven off begins to melt but suificiently close to the focus that the temperature is sufliciently elevated to in itiate the reaction between the sulphur dioxide and the reducing agent, and separating the elemental sulphur formed from the accompanying gases externally of the furnace.

3. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing a fluid reducing agent into the furnace charge at a point above the combustion zone but suiiiciently close to the focus that the temperature is sufficiently elevated to initiate the reaction between the sulphur dioxide and the reducing agent, providing said reducing agent in amount suitable to reduce the sulphur dioxith th lti Operation Proper, b t ith ideffom the combustion zone and to maina substantial enhancement of the eiiiciency of that operation, by a much desired internal preheating of the charge, simultaneously with the sulphur reco very.

The, term pyrite as used herein is not intended to be limited to true pyrite, FeS but also includes other forms of iron sulfide containing less sulfur than FeS for example, pyrrhotite, also iron sulfides containing nickel and/or copper, and likewise manufactured products, such as mattcs, which consists principally of iron sulfides.

\Vhile water gas, producer gas, natural gas, and atomized petroleum have been specifically referred to in the illustrativermode of procedure disclosed, other fluid reducing agents may be substituted therefor which will likewise provide a reducing gas or vapor to form elemental sulphur from sulphur dioxide.

We claim:

1. In the smelting ofsulphidc ores, the

process of recovering elemental sulphur which comprises, introducing a fluid reducing agent into the furnace charge at a point above the combustion zone but sufficiently close to the focus that the temperature is sufficiently elevated to initiate the reaction between the sulphur dioxide and th reducing agent providing said agent in amount suitable to reduce the sulphur dioxide from the combustionzone to elemental sulphur and to maintain a non-oxidizing atmosphere for the elemental sulphur produced by the reduction and volat-ilization at least while said sulphur is susceptible to existing oxidizing influences, passing said reducing agent and the accompanying gases from the combustion zone through the furnace charge, and separating the elemental sulphur from the accompanying gases externally of the furnace.

2. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing a fluid reducing agent for the sulphur dioxide intothe tain a non-oxidizing atmosphere for the elemental sulphur, and separating the sulphur from the accompanying gases.

l. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing into the furnace charge at point above the combustion zone but sufficiently close to the focus that the temperature is sufiiciently elevated to initiate reaction between the sulphur dioxide and the reducing agent a fluid reducing agent adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat to provide preheating of a substantial portion of the charge by the heat liberated upon re action with the sulphur dioxide, and separating the elemental sulphur from the accompanying gases externally of the furnace.

5. Inthe smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing into the furnace charge at a point above the combustion zonebut sufficiently close to the focus that the temperature is suiiicientl elevated to initiate reaction between the sulphur dioxide and the reducing agent a fluid reducing agent adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat, providing said reagent in su'l'licient amount and at such temperature to reduce the sulphur dioxide from the combustion zone to elemental sulphur while avoiding sintering in the upper portion of the ore charge, and separating the elemental sulphur from the accompanying gases externally of the furnace.

6. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing into the furnace charge at a point above the combustion zone but sufficiently close to the focus that the temperature is sufficiently elevated to initiate reaction between the sulphur dioxide and the reducing agent a fluid reducing agent adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat,

providing an excess of said reducing agent to maintain a non-oxidizing atmosphere for the sulphur liberated by reduction and volatilization, and separating the elemental sulphur from the accompanying gases externally of the furnace.

7. In the smelting of sulphide ores, the process of vrecovering elemental sulphur which comprises, introducing a gas adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat into the furnace charge at a point slightly above the point at which the ore from which the volatile sulphur has been liberated begins to melt but sufficiently close to the focus that the temperature is sulficiently elevated to initiate the reaction between the sulphur dioxide and the reducing agent, passing said reducing gas in'company with the hot gases from the combustion zone up through the ore charge to recover elemental sulphur from the sulphur dioxide and simultaneously preheat the charge, and separating externally of the furnace the elemental sulphur formed.

8. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing a fluid reducing agent into the charge at a point above the combustion zone but sufficiently close to the focus that the temperature is sufliciently elevated to initiate the reaction bet-ween the sulphur dioxide and the reducing agent, passthat the temperature is sufiiciently elevated to initiate the reaction between the sulphur dioxide and thereducing agent a reducing gas containing oxidizable hydrogen and adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat, providing said gas in amount sufficient to reduce the sulphur dioxide from the combustion zone to elemental sulphur, and to maintain a non-oxidizing atmosphere for, the sulphur producedby reduction in volatilization at least for the period while such sulphur is susceptible to existing oxidizing influences, separating the elemental sulphur from the accompanying gases, and passingvt-he residual gases in contact with a suitable cata yst under conditions adapted to recover the remaining combined sulphur, and separating the elemental sulphur formed.

10. In the smelting of sulphide ores, the process of recovering elemental sulphur which comprises, introducing into the furnace charge at a point above the combustion zone but sufficiently close to the focus that the temperature is sufficiently elevated to initiate the reaction between the sulphur dioxide and the reducing agent a fluid reducing agent containing oxidizable hydrogen and adapted to reduce sulphur dioxide to elemental sulphur with the liberation of heat, providing said gas in amount sufficient to reduce the sulphur dioxide from the combustion zone to elemental sulphur and to main tain a non-oxidizing atmosphere for the elemental sulphur entrained, passing said reducing gas in contact with the hot sulphur dioxide from the combustion zone'through the furnace charge whereby said charge will be preheated by the interaction of said gases, and separating the elemental sulphur from ,the accompanying gases externally of the furnace. r a

In testimony whereof we aliix our signatures.

RAYMOND F. BACON. c

'. HENRY T. HOTCHKISS, JR. 

